Hydraulic control system for tractor loader



United States Patent Ofiice 3,250,411 Patented May 10, 1966 3,250,411 HYDRAULIC CONTROL SYSTEM FOR TRACTOR LOADER Karl Salna, Mundelein, Herbert A. Mark, Northbrook, and Carl C. Baker, Mundelein, Iil., assignors to The Frank G. Hough Co., a corporation of Illinois Filed Dec. 23, 1964, Ser. No. 420,681 19 Claims. (Cl. 214-140) This invention relates to the hydraulic control systern for a tractor loader, and more specifically relates to a multiple pressure hydraulic system for operating the boom arms and bucket linkage on a tractor loader.

Excavating vehicles include those generally known as front end tractor loaders which would make use of the invention described herein. However, it is understood that this invention can be utilized with a wide variety of machinery in which hydraulic equipment is used to excavate and lift earth or other loads.

In the operation of an earth-digging machine the situation exists when equipment must move the bucket into a pile of earth, break out the bucket from the pile, and then lift the bucket to the required height for dumping into an adjacent earth hauler or truck. In operating through these cycles the power requirements vary greatly. Thus when the bucket is going into the earth pile and breaking it loose, the total hydraulic ower requirement is greater than when carrying the load through the intermediate lifting positions. Also the hydraulic power requirement increases as the bucket approaches the high lift position. This occurs because of the geometry of the boom arms and the hydraulic ram. The force of the ram acts through a shorter moment arm as the high lift position is approached. Another problem encountered in excavating is that where a loader operates at only one speed, inefficiency and loss of time in the loading operation results. The efforts to overcome these disadvantages have resulted in dual pump unloading valves for two-speed operation of the hydraulic rams. However, an objectionable feature inherent in these types of unloading valves is that the valves are responsive to only one predetermined pressure. Thus previous valves direct the combined flow of both pumps to the rams for high speed operation until break out conditions, or heavy loads, are encountered whereupon the valve operates to direct flow from only one of the pumps tothe rams. There is no provision to allow low or high speed operation dependent upon three different pressures in the system.

Accordingly it is an object of this invention to provide a dual pump unloading .valve which results in improved lifting characteristics.

It is a further object of this invention to provide a dual pump unloading valve which controls the hydraulic power to match the lifting requirements of the hydraulic rams.

It is another object of this invention to provide a tractor loader with a hydraulic control system which operates through a first phase in which one pump is in the system during low hydraulic pressure, through a second phase in which two pumps are in the system during normal hydraulic pressure, and through a third phase in which one pump is in the system during high hydraulic pressure.

A further advantage in applicants novel invention is that with articulated vehicles the unloading valve may be located near the pumps and reservoir on the rear sec tion of the vehicle so that the low pressure lines need not extend to the front section. Thus fluid line losses are reduced and the hydraulic fluid operates at a lower temperature with a consequent saving in available horse power. It therefore is an object of this invention to allow a substantial reduction in fluid line losses by providing a new and improved unloading valve which may be located on the rear section of an articulated vehicle.

The situation frequently exists where it is desirable to maintain a slow lift speed even though the hydraulic pressure has exceeded the value which would shift the unloading valve for high speed operation. This may occur when the loader is moving into hard material such as blasted lime stone or rocks. Thus the operator will find it convenient to maintain a slower speed of the lifting mechanism until the bucket is filled, whereupon the faster speed operation can be used to bring the bucket to the high lift position. With presently existing loaders the bucket may rapidly come out of the pile while only partially full, with a consequent reduction in efiiciency. This occurs because with conventional unloading valves the speed of the boom arms is dependent solely on the pressure developed in the hydraulic line. .It is desirable if the operator can adjust the control device such that the unloading valve initiates high speed operation only after the boom arms have reached a predetermined height. Therefore, it is a further object of this invention to provide an unloading valve which the operator may override or render inoperative.

It is yet another purpose to provide a dual pump unloading valve which connects one or both pumps to the hydraulic rams for operating a lifting device responsive to predetermined pressures in the lines and which is selectively rendered inoperable to connect both pumps to the rams.

It is still another purpose of this invention to provide a dual pump unloading valve which is rendered operable to provide high speed lifting of the load only after the boom arms are raised to a predetermined position.

Still another purpose of this invention is to provide a dual pump unloading valve which may be rendered inoperative in response to the position of the boom arms and in which the point in which the valve is rendered inoperative may be readily adjusted.

Still another object is to provide a dual pump unloading valve in which the valve is rendered inoperative in response to operating means such as an electrical current and in which said electrical current is supplied in response to the position of the boom arms.

Other objects of this invention will become apparent from the following description and drawings. The accompanying drawings illustrate several examples of the invention, it being understood that changes may be made in the precise embodiment of the disclosed invention as come within the scope of the claims.

In the drawings:

FIGURE 1 is a side elevation view of a tractor loader showing a hydraulic system with an unloading valve, relief valve and adjust-able linkage means positioned according to one embodiment of the present invention;

FIGURE 2 is a detailed sectional view of the loading valve of FIGURE 1; and

FIGURE 3 is a diagrammatic view of a modified form of the adjustable linkage means of FIGURE 1 in which an electrical circuit is employed.

3 Referring now to the accompanying drawings, in whic like reference characters designate like parts throughout the several views, FIGURE 1 shows a complete tractor loader with the well-known loader attachment consisting of boom arms 12 which carry the bucket assembly 14. The hydraulic system for operating the boom includes extensible hydraulic rams 16. The bucket assembly is operated through linkage means 20 which are in turn operated by extensible ram 18. Hydraulic fluid under pressure to operate the rams is supplied by high pressure pump 26 and low pressure pump 24. Both pumps are of the conventional vane type construction and are selected so that pump 26 delivers a high pressure, small flow rate while pump 24 delivers a low pressure, large flow rate. Prime mover 28 mounted on the tractor loader 10 supplies the turning force to operate the pumps. The pumps withdraw supply fluid from hydraulic reservoir 22 through common hydraulic conduit 30. Low pressure fluid is directed from pumps 24 through conduit 32 to unloading valve 36, while high pressure fluid is directed from pump 26 through conduit 34 to unloading valve 36. Conduit 56 provides a return line from the unloading valve 36 to the reservoir 22. Hydraulic control valve 38 is of the wellknown open center spool valve type and controls the operation of the boom arms and bucket assembly. Conduit 48 directs fluid from unloading valve 36 to control valve 38 while conduit 54 provides a return line to reservoir 32. Manually operated control link-age 44 operates the position of spool valve 40 which in turn directs fluid through lines 50 to rams 16 to raise and lower the boom arms. Manually operated control linkage 46 operates spool valve 42 which in turn directs fluid through lines 52 to ram 18 to control the position of bucket 14. Relief valve 62 is provided to selectively render inoperative unloading valve 36. Relief valve 62 can be of the open-closed type and receives fluid from unloading valve 36 through conduit 58 while directing fluid to reservoir 22 through conduits 60 and 56. In the embodiment shown in FIGURE 1 relief valve 62 is operated by the boom arms through a cam linkage consisting of arm 68, cam 66 and cam follower 64. Cam follower 64 may be adjustable to selectively vary the predetermined position of the boom arms which will operate relief valve 62. The cam linkage may conveniently be located in the operators compartment so that said predetermined position may easily be varied.

FIGURE 2 shows the improved unloading valve designated generally as 36. Valve body -70 houses upper conduit 72 which provides direct fluid communication between conduits 34 and 48. Located intermediate the valve housing in the upper conduit is poppet valve 78 which is biased toward closure by spring 80. With the poppet valve in the open position vertical-bore 78 provides. fluid communication between upper conduit 72 and lower chamber 74. Lower chamber 74 may be a horizontal bore in valve housing 70 which is adapted to receive piston 96. Vertical bore 76 extends to the lower portion of housing 70 and is in fluid communication with conduit 32. Return conduit 56 extends up through the lower margin of housing 70 in fluid communication with chamber 74. Piston 96 is slidably carried in chamber 74 and supports opposed spacedapart piston heads 98 and 100. Piston head 98 has a larger base area than piston head-100. In the position of the piston shown in FIGURE 2 piston head 98 is spaced from the left end of chamber 74 to define a space for biasing spring 99 which urges the piston to the right position. A pilot relief valve 86 is provided in the unloading valve 36. Conduit 82 provides fluid communication between conduit 72 and pilot re- .lief valve 86. Spring 88 urges the pilot relief valve towards its closed position. Chamber 84 receives fluid from conduit 82 when the pilot relief valve is opened,

' and may be a bore through piston 96. An orifice 94 is provided in bleed line 92 at any convenient location. The bleed line 92 is shown as communicating the left end of chamber 74 with the central section of chamber 74 but may also be a conduit from chamber 84 to return conduit 56. Control chamber 104 is provided to supply the operating force to move piston 96- to the left. Control conduit 102 provides fluid communication between conduit 48 and chamber 104, While orifice 106 is positioned in conduit 102 at any convenient location to control the rate of fluid flow into chamber 104. Control chamber 104 is in turn in fluid communication with conduit 58.

FIGURE 3 relates to another embodiment of the invention of FIGURES l and 2 and shows a schematic wiring diagram of the electrical control system for operating the relief valve 62 responsive to the position of boom 12. Adjustable linkage 118, which may be of the cam type as shown in FIG. 1, interconnects boom arm 12 with on-off switch 112. The linkage 118 may be adjusted to vary the position at which the boom 12 will throw switch 112. Electrical supply source 116 is connected to ground by line 128 and through line 126 to manually operated on-oif switch 114. Switch 114 is connected through line 124 to switch 112 which is in turn connected through line 122 to solenoid 110 and then to ground through line 120. Solenoid 110 operates relief valve 62 which interconnects conduits 58 and 60.

In operation it is assumed that the bucket is in the lowered position and ready to enter an earth pile. With the boom in the lowered position relief valve 62 is opened through operation of arm 68, cam 66 and adjustable cam follower 64. With relief valve 62 open any pressure in chamber 104 will be fed through conduit 58 to conduits 60, 56 and reservoir 22. Prime mover 28 operates pumps 24 and 26 to supply fluid from reservoir 22 to conduit 30. Pump 24 receives fluid from conduit 30 and supplies low pressure fluid through conduit 32 to unloading valve 36. As seen in FIGURE 2, piston 96 of the unloading valve is urged toward its right position by spring 99 because of the absence of any pressure in chamber 104. Bleed line 108 will bleed out any fluid in the right portion of chamber 74 to conduit 56. With the piston in the position shown in FIG- URE 2 low pressure fluid from conduit 32 will enter chamber 74 and exit through conduit 56 and return back to reservoir 22. Meanwhile, pump 26 will deliver high pressure fluid through conduit 34 to conduit 72. Poppet valve 78 is urged toward closure by spring and thus fluid is directed from conduit 72 to conduit 48 and then to hydraulic control valve 38 for operation of the hydraulic rams. The rams are now operating at a slow speed. When the bucket 14 encounters an increased load the hydraulic rams will transmit an increased pressure back through hydraulic control valve 38 and into conduit 48. This increased pressure will be transmitted through conduit 102 to chamber 104 and back to conduit 58 without shifting the piston. Thus with the boom in the low position low speed operation is maintained. When the boom has been raised to the first predetermined position arm. 68, cam 66 and cam follower 64 will operate relief valve 62 to a closed position. With relief valve 62 closed conduit 58 will no longer transmit fluid from unloading valve 36 back to the reservoir. Thus,'when an increased load is received by bucket 14 with the boom at or past the first predetermined position fluid pressure transmitted by the rams through the hydraulic control valve to conduit 48 will be transmitted through conduit 102 to chamber 104. The increased pressure in chamber 104 will operate on piston head 100 and shift piston 96 to the left position. With the piston in the left posi tion the unloading valve no longer unloads low pressure pump 24 through conduits 32 and 56 back to reservoir 22. The opening to conduit 56 from chamber 74 is now closed. The fluid coming from pump 24 through conduit 32 will pass from chamber 74 to bore 76 and through poppet valve 78 into conduit 72. The combined flow of fluid from pumps 24 and 26 will now pass from conduit 72 into conduit 48 for delivery to hydraulic control valve 38 and therefore the rams will operate at a faster speed. It is appreciated that spring 99 may be selected so that unloading valve 36 operates to give combined flow from both pumps when the pres sure in conduit 48 has built up to any predetermined value. In a preferred embodiment of this invention it has been found that with pump 26 operating at a maximum pressure of 2500 psi. and pump 24 operating a maximum pressure of 2000 p.s.i. that unloading valve 36 may desirably operate to give combined flow from both pumps when the resistance in line 48 has built up to 250 psi. It has also been found expedient to construct cam follower 64 so that its length may be adjusted so that relief valve 62 operates when bucket 14 moves past a desired distance from the ground within the range of O to 4 feet, as an example.

With the combined flow from both pumps being delivered to the hydraulic rams the booms will raise the bucket rapidly towards the high lift position. However, because of the geometry of the loader construction the effective moment arm of the rams operating the boom arms decreases towards the high lift position. Therefore, increasing pressure is needed from the rams. To supply this increased pressure it is desirable that the unloading valve operate to direct only high pressure flow from pump 26 while unloading pump 24 to reservoir 22. To achieve this function pilotrelief valve 86 is provided. In the preferred embodiment previously described pilot relief valve 86 will operate to unload pump 24 when pressure in line 48 reaches 2000 psi. This pressure is transmitted through conduit 72 into pilot relief line 82 and the pressure then overcomes the biasing force of spring 88 to open relief valve 86. The fluid then enters chamber '84 and into conduit 90 where it is transmitted 'into the left portion of chamber 74 to act against piston head 98. Because the effective area of piston head 98 is larger than the effective area of piston head 100 then piston 96 will move toward the right position. With piston 96 in the right position the opening from chamber 74 into conduit 56 is exposed so that fluid from pump 24 coming through conduit 32 to chamber 74 will be unloaded through conduit 56 back to reservoir 22. The result is that the unloading valve 36 now supplies high pressure hydraulic fluid from pump 26 into conduit 48 to hydraulic control valve 38 for slow speed operation of the rams.

As the piston 96 moves to the right position any fluid contained in the space between the right hand portion of piston 96 and valve body 70 will be drained through bleed line 108 into conduit 56. Pilot relief bleed line 92 is also provided to give fluid communication between pilot relief chamber 84 and the central portion of chamber 74. This is provided so that any fluid remaining in chamber 84 or in the space between piston head 98 and the left end of chamber 74 will not prevent movement of piston 96 to the left position but instead will drain through pilot relief bleed line 92 into chamber 74. Orifice 94 is provided in pilot relief bleed line 92 so that pressure may build up to a sufiicient value to act against piston head 98 when the pilot relief valve operates. It is understood that spring 88 which urges pilot relief valve 86 to its closed position may be selected to allow the pilot relief valve 86 to open at any desired pressure, depending upon the operating characteristics desired in the vehicle.

With the boom arms and bucket in the maximum high lift position the operator will operate control linkage 46 so that bucket 14 will dump the load as desired. The operator will then operate control linkage 44 so that the boom arms will be brought down to the lowered position. As the boom arms are lowered pressure in the hydraulic lines leading to conduit 48 will decrease so that pilot relief valve 86 will close. While the pressure in conduit 48 is still above 250 p.s.i. this pressure is transmitted to conduit 102 and into chamber 104 so that piston 96 is moved to the left position. The valve 36 now directs combined fluid flow to hydraulic control valve 38 as described above.

The boom arms are lowered until arm 68, cam 66 and the cam follower 64 again operate relief valve 62 so that conduit 58 is opened to reservoir. This sequence of operations will relieve pressure from chamber 104 so that spring 99 will urge piston 96 to the right position wherein pump 24 is unloaded through conduit 32, chamber 74 and conduit 56 back to reservoir 22. Unloading valve 36 now operates to deliver only fluid from high pressure pump 26 so that low speed operation of the loader results. The loader is now ready to receive a second load and go through another cycle of operations as previously described.

FIGURE 3 describes another embodiment of this invention wherein an electrical circuit is provided to operate relief valve 62. In FIGURE 3 it is seen that solenoid directly operates relief valve 62 to the open or closed position. Operation of solenoid 110 is in turn controlled by the position of boom arm 12 so that relief valve 62 is opened and closed in relation to the position of boom arm 12 in a similar manner to that described in connec tion with FIGURE 1. Linkage 1*18 connecting boom arm 12 to switch 112 may be of any well known adjustable linkage such as a cam with a cam follower of adjustable length. Assuming that the operator has closed switch 114, with boom 12 in the low position linkage 118 will have closed switch 112. This will complete the electrlcal circuit from power source 116 to solenoid 110 and then to ground. With solenoid 110 energized relief valve 62 is'opened so that conduit 58 is opened to conduit 60 and then back to conduit 56 and reservoir 22. This operation will provide the selective slow speed operation described in connection with FIGURES 1 and 2. As boom 12 moves past the first predetermined position switch 112 is opened breaking the circuit to solenoid 1'10 and thus closing valve 62. This will in turn 'close conduit 58 so that unloading valve 36 is now operative to provide two-speed lifting'of the boom arm.

From the foregoing it will be noted that applicants have provided a novel multiple pressure loader system which provides either high fluid pressure for break out" force or combined fluid flow from two pumps for high speed Iboom lift, While further providing a novel relief valve which allows selective determination of the point of bucket height in which two-speed operation becomes effective.

Various changes may be made in the specific embodiments of this invention hereinabove described without departing from the spirit of the invention as defined in the attached claims.

What is claimed is:

1. In a tractor loader having a pivotal boom, the combination comprising hydraulic motor means for pivoting said boom, a load-engaging attachment mounted on said boom, afirst source of fluid pressure connected with said motor means, :a second source of fluid pressure adapted for connection with said motor means, said second source being normally disconnected from said motor means, valve means responsive to a first resistance of said load for connecting said second source with said motor means and responsive to a second resistance of said load greater than said first resistance for disconnecting said second source from said motor means.

2. In a tractor loader as defined in claim 1 in which said valve means is responsive to a first predetermined 7 pressure in said motor means for connecting said second source with said motor means and to a second predetermined pressure in said motor means higher than said firstpressure for disconnecting said second source from said motor means.

3. In a tractor loader as defined in claim 1 in which the connection between the first source and said motor means comprises a conduit, said valve means including pressure responsive piston means movable between a first position disconnecting said second source from said motor means and a second position connecting said second source to said motor means, said valve means being responsive to a first predetermined pressure in said conduit for moving said piston to said second position, and

responsive to a second predetermined pressure in said conduit higher than said first pressure for moving said piston to said first position.

4. In a tractor loader as defined in claim 1 further comprising operating means for selectively preventing said valve means from connecting said second source with said motor means.

5. In a tractor loader having pivotal boom, the combination comprising hydraulic motor means for pivoting said boom, a load-engaging attachment mounted on said boom, a first source of fluid pressure connected with said motor means, a second source of fluid pressure, valve means responsive to a first resistance of said load for connecting said second source with said motor means and responsive to a second resistance of said load for disconnecting said second source from said motor means, and operating means for selectively preventing said valve means from connecting said second source with said motor means, said operating means being responsive to a first pivot angle of said boom for preventing said valve means from connecting said second source with said motor means.

6. In a tractor loader as defined in claim 5 further comprising adjusting means for selectively varying said first pivot angle to which said operating means responds.

7. In a tractor loader as defined in claim 3 further comprising other means for preventing movement of said piston to said second position.

8. In a tractor loader having a pivotal boom, the com- :bination comprising hydraulic motor means for pivoting said boom, a load-engaging attachment mounted on said boom, a first source of fluid pressure connected with said motor means, a second source of fluid pressure,'valve means responsive to a first resistance of said load for connecting said second source with said motor means and responsive to a second resistance of said load for disconnecting said second source from said motor means, said connection between the first source and said motor ,means comprising a conduit, said valve means including pressure responsive piston means movable between a first position disconnecting said second source from said motor means and a second position connecting said second source to said motor means, said valve means being responsive to a first predetermined pressure in said conduit for moving said piston to said second position and responsive to a second predetermined pressure in said conduit for moving said piston to said first position, other means for preventing movement of said piston to said second position, and additional means connected with said boom for operating said other means in response to a predetermined position of said boom.

9. In a tractor loader having a pivotal boom, the combination comprising hydraulic motor means for pivoting said boom, a load-engaging attachment mounted means and responsive to a second resistance of said load for disconnecting said second source from said motor means, said'connection between the first source and said line.

motor means comprising a conduit, said valve means including pressure responsive piston means movable between a first position disconnecting said second source from said motor means and a second positionconnecting said second source to said motor means, said valve means being responsive to a first predetermined pressure in said conduit for moving said piston to said second position and responsive to a second predetermined pressure in said conduit for moving said piston to said first position, other means for preventing movement of said piston-to said second position, a source of electrical power, solenoid means for operating said other means, switch means for connecting said source of power to said solenoid means, and linkage means for operating said switch means in response to a predetermined position of said boom.

10. In a tractor loader having a pivotal boom supporting a movable bucket, the combination comprising hydraulic motor means, a first pump supplying fluid at'a selected pressure, a second pump supplying fluid at a pressure lower than said selected pressure, a first conduit connecting said first pump to said hydraulic motor means, an unloading valve with a first chamber connecting the pressure side of said second pump to said first conduit, 21 second conduit connecting said first chamber to a hydraulic reservoir, a piston slidable in said chamber to first and second positions, biasing means urging said piston to said first position, said piston opening said second conduit in said first position and closing said second circuit in said second position, a second chamber, a third conduit connecting said first conduit with said second chamber, said piston slidable in said second chamber and adapted to move to said second position when a first predetermined pressure is present in said second chamber, a third chamber, valve means connecting said conduit with said third chamber for admitting fluid into said third chamber at a second predetermined pressure in said conduit, said piston slidable insaid third chamber and adapted to move to said first position when the fluid force in said third chamber and the biasing means overcome the fluid force in said second chamber.

11. In a tractor loader as defined in claim 10 in which the eifective area of the piston upon which the fluid acts in the second chamber is less than the effective area of the piston upon which the fluid acts in the third chamber.

12. In a tractor loader as defined in claim 10 and further comprising a bleed line connecting said third chamber 'with said first chamber and an orifice in said bleed 13. In a tractor loader as defined in claim 10 and further comprising an orifice in said third conduit.

14. In a tractor loader as defined in claim 10 and further comprising relief valve means for selectively relieving fluid pressure from said second chamber.

15. In a tractor loader as defined in claim 14 in which said relief valve means includes a relief conduit connected to said second chamber for closing said relief conduit in a closed position and connecting said relief conduit with said reservoir in an open position.

16. In a tractor loader as defined in claim 14 in which said relief valve means in responsive to the position of said boom arms.

17. In a tractor loader having a boom carrying a hydraulically operated loadingattachment, hydraulic operating means for operating said attachment in a first speed, and a second speed higher than said first speed, selector means connected with said operating means for selecting one of said speeds, and control means for selectively'preventing said selector means from changing from the first speed to the second speed.

18. In a tractor loader having a boom carrying a hydraulically operated loading attachment, hydraulic operating means for operating said attachment in at least two speeds, selector means connected with said operating means for selecting one of said speeds, control means for selectively preventing said selector means from changing to the other of said speeds, said control means being responsive to the position of said boom.

19. In a tractor loader as defined in claim 18 including adjusting means connected with said control means for selectively determining the position of the boom at which the control means prevents operation of said selector means.

References Cited by the Examiner UNITED STATES PATENTS HUGO O. SCHULZ, Primary Examiner. 

5. IN A TRACTOR LOADER HAVING PIVOTAL BOOM, THE COMBINATION COMPRISING HYDRAULIC MOTOR MEANS FOR PIVOTING SAID BOOM, A FIRST SOURCE OF FLUID PRESSURE CONNECTED WITH BOOM. A FIRST SOURCE OF FLUID PRESSURE CONNECTED WITH SAID MOTOR MEANS, A SECOND SOURCE OF FLUID PRESSURE, VALVE MEANS RESPONSIVE TO A FIRST RESISTANCE OF SAID LOAD FOR CONNECTING SAID SECOND SOURCE WITH SAID MOTOR MEANS AND RESPONSIVE TO A SECOND RESISTANCE OF SAID LOAD FOR DISCONNECTING SAID SECOND SOURCE FROM SAID MOTOR MEANS, AND OPERATING MEANS FOR SELECTIVELY PREVENTING SAID VALVE MEANS FROM CONNECTING SAID SECOND SOURCE WITH SAID MOTOR MEANS, SAID OPERATING MEANS BEING RESPONSIVE TO A FIRST PIVOT ANGLE OF SAID BOOM FOR PREVENTING SAID VALVE MEANS FROM CONNECTING SAID SECOND SOURCE WITH SAID MOTOR MEANS. 